1. Field of the Invention
The present invention generally relates to semiconductor device packages, and more particularly, to thin semiconductor device packages comprising a circuit board, manufacturing methods thereof, and stack packages employing the same.
2. Description of the Related Art
Semiconductor device packages need to be faster, smaller, and thinner in order to meet the increasing demands of miniaturization and multi-function capability for use in electronic apparatus. Ball Grid Array packages (hereinafter referred to as “BGA package”) have been developed in an attempt to satisfy this trend. A BGA package is a type of surface mount package that uses a circuit board and solder balls or solder bumps, instead of lead frames, for electrical connection to the external apparatus. With the BGA package, the mounting density is improved and thus, the number of the input/output (I/O) pins increase.
FIG. 1 is a cross-sectional view depicting a conventional BGA package, more particularly a PBGA (Plastic Ball Grid Array) package manufactured by Hitachi. The package 20 includes a semiconductor chip 21, having an upper active surface 21a where the ICs are formed. The rear surface 21b of the chip 21 is attached to an upper surface 22a of a circuit board 22 having land patterns 23. The semiconductor chip 21 is electrically interconnected to the land patterns 23 using a wire-bonding method with Au (gold) wires 24, and the land patterns 23 are connected to bumps 25 which are formed on a lower surface 22b of the circuit board 22 for electrically connecting to the external apparatus. The electrical interconnections to the semiconductor chip are encapsulated with a molding compound 26 in order to protect them from external environmental stress.
Because the BGA package 20 utilizes bumps 25 as the external connection means throughout the lower surface of the circuit board 22, it has an advantage in that a semiconductor chip having an increased number of the I/O pins can be easily packaged. The pitch between the external connection means of the BGA package is usually in a range from 1.27 mm to 1.50 mm. However, micro-BGA packages or chip-scale packages (CSPs) having a pitch of 1.0 mm or less have been developed.
Although the BGA package is very effective for manufacturing smaller sized products having multiple pins, when the external connection means such as the solder balls or solder bumps are attached to the package, problems such as imprecise attachment, or defects in the solder balls or the solder bumps themselves can occur. Rework is cumbersome and test inspections with the naked eye are difficult. Further, the costs for forming the external connection means and manufacturing the circuit board are more expensive compared to other packages. For example, although a BGA package can be advantageously employed for packages having 200 or more pins, it is disadvantageous for memory chips or other types of micro chips having 100 or fewer pins.